Conventional wide-format laser printers have generally been limited to printing on A3 (297×420 mm) size media in portrait mode with a scan line length not exceeding about 317 millimeters. Therefore, the size of images printed with conventional wide-format laser printers is typically about the size of a ledger-sized sheet of paper, or about 11×17 inches. Commercial printing businesses would benefit significantly from a wide-format laser printer that could print larger images onto larger media. For example, a printer with a scan length of 614 mm could print an image 594 mm wide on C2 or B2 size media. Such an image would be twice as wide as the usual 297 mm wide A3 image. (Note that, in this example, the scan length exceeds the nominal image width by 10 mm at each end of the scan to allow for image position correction, crop mark printing, etc.) One way to increase the image width in a wide-format laser printer is to design a “scaled-up” version of a current laser scanner system such that the scaled-up scanner is capable of scanning a wider image field (e.g., 614 millimeters) in one scan pass. However, preliminary analysis of such scaled-up laser scanner designs demonstrates various problems. One such problem with scaling up an existing scanner design to a larger format is that the residual aberrations in the optical design scale in proportion to the scan length, thereby increasing the geometric focused spot size, while the diffraction-limited spot size remains constant. Consequently, a scanner design which is initially diffraction limited (i.e., which has a focused spot size very close to the theoretical minimum), will not ordinarily remain diffraction limited when doubled in size. Instead, the spot size will increase because the optical performance is now dominated by aberrations rather than diffraction. The result of scaling a just-diffraction-limited scanner by 2×, for example, would be a doubling of both the scan line length and the geometric focused spot diameter. Such a scaling operation does not achieve any increase in the total number of resolvable focused spots in a scan line, and the resulting scanner could not print any more optically resolved pixels in a scan line than the initial system. Achieving a 2× increase in the number of resolvable pixels requires reducing the geometric spot size in the 2× system below the diffraction limit, which requires a new optical design if it can be accomplished at all.
Another problem with simply scaling up an existing scanner design to a larger format is an associated disproportionate increase in cost to produce the scaled-up design. This is true even if we ignore the need to make the scaled-up system optically superior to the original (i.e., parent) scanner in order to control optical aberrations to a level that will enable the scaled-up system to be substantially diffraction limited. As an example of the disproportionate increase in costs, scaling up the linear dimensions of an existing (1×) scanner design by a factor of two increases the production costs for the scaled-up (2×) version by roughly a factor of 8 over the production costs of the original 1× design. This large cost increase is explained by the fact that the volume of any object scales as the cube of its linear dimension. Thus, every part of the 2× scanner has eight times the volume of the corresponding part in the 1× scanner. Like many products, the manufacturing cost for a laser scanner assembly is very roughly proportional to its volume or, equivalently, its weight.
Accordingly, the need exists for a way to increase the printable image width in a wide-format laser printer that avoids the optical problems and added expense associated with scaling up existing optical designs to wider formats.